1. Field of Invention
The present invention relates to a damping control device damping vibration and an engine mount having the damping control device. In particular, the present invention relates to a damping control device filled with a magnetorheological fluid (hereinafter, referred to as a MR fluid) which controls a vibration damping ratio by changing a shear stress of the MR fluid according to a current externally provided, and more efficiently controls the flow of the MR fluid by removing a ‘control invalidity section’, unlike the related art, and an engine mount having the damping control device.
2. Description of Related Art
The MR fluid (magnetorheological fluid) is a suspension which is a synthetic hydrocarbon liquid containing soft magnetic particles, and has the property in that a shear stress is changed depending on the intensity of a peripheral magnetic field.
Application of a device which controls an MR fluid by using a continuous change of a shear stress according to the intensity of a magnetic field to not only a general mechanical device such as a damper and a valve but also a device for a vehicle such as an engine mount and a shock absorber is being attempted.
As shown in FIG. 1A, if there is no magnetic field at the periphery of the MR fluid, the particles dispersed in the MR fluid moves freely, but if a magnetic field is formed at the periphery of the MR fluid, the particles in the MR fluid are aligned perpendicular to the formation direction of the magnetic field. The flow characteristic of the MR fluid is changed depending on the movement of the particles.
Modes of controlling the MR fluid are classified into a flow mode and a squeeze mode according to the relative movement between the formation of the magnetic field and the MR fluid.
The flow mode is a mode which generates a volume flow q of the MR fluid between an upper core and a lower core according to a pressure difference P1-P2 between both sides and provides a current iA to a coil so as to form a magnetic field, thereby aligning the particles of the MR fluid. The volume flow q of the MR fluid is determined by the intensity of the current iA. Therefore, the pressure and flow rate of the MR fluid simultaneously change in a flow path, but there is no pressure externally applied.
In the squeeze mode, a core plate (a pressure applying plate) is disposed between an upper core and a lower core. If an external force F is applied to the pressure applying plate, the pressure applying plate presses the MR fluid such that the MR fluid moves leftward and rightward (in FIG. 1A). At this time, if a current iA is applied to a coil mounted on the upper core, a magnetic field B is formed perpendicular to the movement direction of the MR fluid at the same time as the application of the current to the coil, whereby the shear stress of the MR fluid varies, resulting in a change in the fluidity of the MR fluid. A damping control device using the squeeze mode is a configuration which controls the current applied to the coil so as to vary the volume flow of the MR fluid, thereby damping the vibration of the pressure applying plate receiving the external force F between the upper core and the lower core.
Meanwhile, an engine mount is mounted in an engine room of a vehicle so as to prevent vibration of the engine from being directly transmitted to the body of the vehicle. As the engine mount, a rubber mount using the elasticity of an insulator material and a hydro mount using a fluid elasticity effect by making a hydro liquid filled therein flow according to the elasticity of an insulator are generally used. As shown in FIG. 1B, in the hydro mount, the hydro liquid is contained in an internal space formed by the insulator and a diaphragm, and the internal space is divided into an upper fluid chamber and a lower fluid chamber by an orifice plate placed therein. The orifice plate has a ring-shaped (or other shapes of) flow path which is formed inside along the edge of the orifice plate and through which the hydro liquid flows. At the center of the orifice plate, a decoupler may be additionally mounted. Further, the insulator is connected to a stud which is connected to a bracket of the engine. Therefore, if elastic compression and restoration of the insulator made of an elastic material are repeated according to a load applied to the stud, the hydro liquid flows between the upper fluid chamber and the lower fluid chamber through the flow path. The flow of the hydro liquid vibrates the decoupler. Therefore, vibration in a high frequency band vibration is damped by the vibration of the decoupler and vibration in a low frequency band is damped by the flow of the hydro liquid through the flow path.
However, the hydro mount exhibits an effective vibration insulation performance only at a resonance point. For this reason, a hydro mount which is filled with an MR fluid and has a coil additionally mounted therein to more actively control vibration according to the running condition of a vehicle has been developed.
Meanwhile, a damping control device according to the related art which controls an MR fluid by using the squeeze mode or a hydro mount filled with an MR fluid operates as shown in FIG. 1C.
As shown in FIG. 1C, an upper core and a lower core are disposed to be spaced apart from each other so as to form a flow path through which the MR fluid can flow. The upper core is supported by a spring to be moveable upward and downward (to perform the same function as the core plate shown in FIG. 1A), and a coil is mounted on the lower core. When an external force F is applied to the upper core, if a current is applied to the coil, a magnetic field is formed at the periphery of the coil to be perpendicular to the movement direction of the MR fluid so as to increase the shear stress of the MR fluid. Therefore, the movement of the MR fluid is reduced according to the movement of the upper core. In order to implement this function, (as shown in FIG. 1A), it is necessary to align the particles in the MR fluid to be perpendicular to the flow direction. To this end, the flow direction of the MR fluid should be perpendicular to the formation direction of the magnetic field.
However, according to the related art, in a ‘control validity section’ (in which the magnetic field passes through the MR fluid), the magnetic field is perpendicular to the flow direction of the MR fluid, but in the ‘control invalidity section’ (in which the magnetic field does not pass through the MR fluid), the magnetic field is formed in parallel to the flow direction of the MR fluid so as not to pass through the MR fluid, resulting in a reduction in the efficiency of MR fluid control.
Therefore, the particles in the MR fluid are aligned perpendicular to the formation direction of the magnetic field only in a partial section of the entire flow path. For this reason, in order to provide the required performance, the reduced control efficiency is recovered by increasing a current value applied to the coil or lengthening the flow path. However, this results in an increase in the size and an increase in the amount of heat generation.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.